Title: Plot The Support Vector Classifier's Hyperplane
Slug: plot_support_vector_classifier_hyperplane
Summary: How to plot the support vector classifier's hyperplane in Scikit-Learn
Date: 2017-09-22 12:00
Category: Machine Learning
Tags: Support Vector Machines
Authors: Chris Albon

Preliminaries



In [1]:

    
# Load libraries
from sklearn.svm import LinearSVC
from sklearn import datasets
from sklearn.preprocessing import StandardScaler
import numpy as np
from matplotlib import pyplot as plt

Load Iris Flower Data



In [2]:

    
# Load data with only two classes and two features
iris = datasets.load_iris()
X = iris.data[:100,:2]
y = iris.target[:100]

Standardize Features



In [3]:

    
# Standarize features
scaler = StandardScaler()
X_std = scaler.fit_transform(X)

Train Support Vector Classifier



In [4]:

    
# Create support vector classifier
svc = LinearSVC(C=1.0)

# Train model
model = svc.fit(X_std, y)

Plot Decision Boundary Hyperplane

In this visualization, all observations of class 0 are black and observations of class 1 are light gray. The hyperplane is the decision-boundary deciding how new observations are classified. Specifically, any observation above the line will by classified as class 0 while any observation below the line will be classified as class 1.



In [7]:

    
# Plot data points and color using their class
color = ['black' if c == 0 else 'lightgrey' for c in y]
plt.scatter(X_std[:,0], X_std[:,1], c=color)

# Create the hyperplane
w = svc.coef_[0]
a = -w[0] / w[1]
xx = np.linspace(-2.5, 2.5)
yy = a * xx - (svc.intercept_[0]) / w[1]

# Plot the hyperplane
plt.plot(xx, yy)
plt.axis("off"), plt.show();